1. Use of Simplex Satellite Configurations to support Internet Traffic
Geoff Huston
Telstra Internet
March 1998 1

2. Configuration of Simplex Circuit
Teleglobe
Simplex 45M satellite
circuit
Cisco 7507
Internet
Cisco 7507
Telstra 3

3. IP Configuration Interconnection by
unidirectional satellite link
Internet-based return path
End to end reachability signaling via BGP4 protocol keepalive functionality 4

4. Asymmetric BGP Keepalive flow
Route
Advertisements
Traffic
Flow
Any break in the unidirectional circuit will cause a BGP keepalive failure, which in turn will cause the BGP session to fail. This eliminates the need for an HDLC keepalive signal along the satellite path 5

5. Internet Configuration
Telstra and Teleglobe connect exclusively via a simplex 45M satellite circuit
Telstra uses cable circuits to connect to MCI and AT&T in North America
Teleglobe uses cable circuits to connect to MCI and other ISPs and exchange points in North America 6

6. Internet Configuration
Teleglobe
AS6453
Simplex Satellite Circuit
Internet
Exchanges & Transit
Telstra
AS1221
MCI
AS3561
Duplex Cable Circuits
AT&T
AS5727 7

7. Router Configuration
Telstra and Teleglobe use Cisco 7500 routers to manage the simplex satellite circuit at the IP level
The routers are configured to use multihop BGP4 in an asymmetric circuit configuration, to allow Telstra to pass routes to the Teleglobe router
The Teleglobe router announces these BGP-learned routes into the Internet from this router
On circuit failure the BGP session is closed, and the corresponding route announcements are withdrawn, causing traffic to revert back to available cable circuits in a backup configuration 8

8. Generic cisco configuration for the simplex sender
Sender configuration
Generic cisco configuration for the simplex sender
version 11.2 !
interface Loopback3
ip address
interface Ethernet0
ip address
interface Serial0
ip address
no keepalive
ignore-dcd
router bgp 50
timers bgp 5 30
neighbor remote-as 25
neighbor ebgp-multihop 10
neighbor update-source Loopback3
ip route Serial0 9

9. Receiver configuration
Generic cisco configuration for the simplex receiver
version 11.1 !
interface Loopback3
ip address
interface Ethernet0
ip address
interface Serial0
transmit-interface Ethernet0
ip address
no keepalive
ignore-dcd
router bgp 25
timers bgp 5 30
redistribute static
neighbor remote-as 50
neighbor ebgp-multihop 10
neighbor update-source Loopback3
ip route
ip route 10

10. Configuration Features
BGP4 set to multihop configuration, linking loopback addresses as BGP peers
Reciever set to associate ethernet as the transmit interface via cisco ‘transmit interface” interface
remote loopback address is statically loaded into the router
BGP timers brought down to 5 second keepalive and 30 second holddown (this may vary according to the characteristics of the return cable path)
Note that NO return path tunnel is used in this configuration 11

11. Circuit Stability Tests
Stability of BGP achieved
Time to propagate serial line break to BGP
35 seconds
Time to detect restoration of serial line to BGP
10 seconds 12

12. Interface performance
Cisci interface statistics dump for 3 weeks, 5 days of operation
Hssi6/0 is up, line protocol is up
Hardware is cxBus HSSI
Internet address is /30
MTU 4470 bytes, BW Kbit, DLY 200 usec, rely 255/255, load 1/255
Encapsulation HDLC, loopback not set, keepalive not set
Last input 00:00:00, output 3w5d, output hang never
Last clearing of "show interface" counters 3w5d
Queueing strategy: fifo
Output queue 0/40, 0 drops; input queue 0/75, drops
5 minute input rate bits/sec, 933 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
packets input, bytes, 1 no buffer
Received broadcasts, 0 runts, 0 giants 0 parity
input errors, CRC, frame, overrun, 0 abort
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 applique, 3 interface resets
0 output buffer failures, 0 output buffers swapped out
116 carrier transitions 13

13. Interface performance
Measured on a 3 week 5 day period
Line error rate
less than 0.02% packet error rate
Dropped packets
less than 0.002% packet drop rate in receiver router queue 14

14. Internet performance Test of Delay, Packet loss and Throughput
Tests were conducted using 50 packet ping sequences every 300 seconds, logging packet loss and round trip delay. Throughput was measured using SNMP polling of interface octet counters on the receive end.
The environment constructed here is perhaps one of the more challenging environments where a simplex satellite circuit can be deployed. The two operators have no other direct Internet connection other than the simplex circuit. Ping packets in the reverse direction have to transit a third party to complete the loop, so that ping-based measurements of the overall performance impact of the simplex satellite circuit have to recognise the impact of the third party transit.
Overall the test results indicate that the simplex satellite circuit itself performs well in an Internet configuration. 15

15. Ping Round Trip time measurements
Delay Measurements
Ping Round Trip time measurements
Symmetric ping - Australia - US East coast - cable circuits
Asymmetric ping - Australia to US East coast - cable
US East coast to Australia - satellite 16

16. Delay Measurements
Propagation Delay rises from 291 ms cable symmetric to 449 ms cable and satellite asymmetric circuits
Satellite hop induces no additional variation in delay (no increased jitter component) 17

17. Ping Loss Measurements
Symmetric ping - Australia - US East coast - cable circuits
Asymmetric ping - Australia to US East coast - cable
US East coast to Australia - satellite 18

18. Ping Loss Measurements
While there is some variation between symmetric cable path ping packet loss and asymmetric cable / satellite ping packet loss, no appreciable quantum loss degradation was visible on the asymmetric path.
Loss events are attributable to engineering within the transit networks, as distinct from loss caused by router queue exhaustion on the satellite transmission side 19

19. Throughput Measurements
Peak load tested to date on the circuit is 20Mbps.
Average load tested is 5Mbps
Current routing configuration uses BGP AS path prepending to use satellite circuit for Teleglobe and connected Teleglobe customers as preferred route. 20

20. Link loads, ping RTT and ping Loss reports can be accessed at:
Link Monitoring
Link Monitoring is undertaken through continuous SNMP polling at 300 second intervals.
Link loads, ping RTT and ping Loss reports can be accessed at: 21